Pressure switches have been conventionally used in order to detect the pressure of lubricating oil and to detect changes in the pressures of portions to be detected, such as the intake manifold pressures and exhaust pressures of engines, crank room pressures, and various controlling actuator working pressures, for example, in automobiles and the like.
FIG. 9 is a cross-sectional view for explaining the configuration of a conventional pressure switch.
In the pressure switch 100, a diaphragm configuration member 107 comprising an upper cover 103, a diaphragm 105, and a lower cover 106 is arranged via an O-ring 108 in the interior of a body portion 102.
An O-ring 109 is placed on the upper portion of the upper cover 103, a guide portion 111 is placed thereon, and a connector portion 112 is put so as to immobilize them. In addition, the outer circumferential stepped portion of the connector portion 112 is swaged with the open end of the body portion 102, whereby they are integrated to form a pressure switch.
An actuating shaft 116 that is slidably held in a through-hole 115 disposed in the center of the guide portion 111 is arranged on the upper part of the diaphragm 105, and its upper end is opposed to an actuation portion 119 of a movable contact plate 117.
The bottom end of the actuating shaft 116 comes into contact with the diaphragm 105 through an opening 120 in the upper cover 103. A first connecting terminal 122 and a second connecting terminal 124 that are bent in generally L-shapes are disposed in the connector portion 112, and one end of the movable contact plate 117 is fixed on an end of the first connecting terminal 122 by swaging.
A movable contact 118 is mounted on the other end of the movable contact plate 117, and a fixed contact 125 is fixed on an end of the second connecting terminal 124 so as to be opposed to the movable contact 118. A micro switch is formed by the fixed contact 125 and the movable contact 118.
The pressure switch 100 configured in such a manner is mounted so that the pressure of the interior of an actuation room 123 in a portion beneath the diaphragm 105 is equal to the pressure of the above-mentioned portion to be detected, and is used.
With increasing the pressure of the portion to be detected, the pressure of the interior of the actuation room 123 is also increased, and the center of the diaphragm 105 gradually rises with the increase. When the pressure becomes not less than predetermined pressure and the center of the diaphragm 105 rises over a neutral position and crosses an invertible region, the center of the diaphragm 105 is inverted and actuated upward, and the diaphragm 105 abuts on the lower end face of the upper cover 103 and stops.
As a result, the actuating shaft 116 moves up to a raised position to push up the movable contact plate 117, the movable contact 118 on its leading end is displaced upward, and the movable contact 118 and the fixed contact 125 become in a non-contact state.
The pressure switch 100, which is referred to as a normally closed type, becomes in a conduction state when the pressure of the portion to be detected is not more than the predetermined pressure (in a normal case) and becomes in a non-conduction state, only when the pressure of the portion to be detected is not less than the predetermined pressure, to thereby make it possible to detect a change in the pressure of the portion to be detected.
Pressure switches include a pressure switch, referred to as a normally open type, which becomes in a non-conduction state when the pressure of a portion to be detected is not more than predetermined pressure (in a normal case) and becomes in a conduction state, only when the pressure of the portion to be detected is not less than the predetermined pressure, to thereby make it possible to detect a change in the pressure of the portion to be detected.
In such a pressure switch, for example, a contact structure 200 in which rivet-type contacts 202a and 202b are places to be opposed to each other as illustrated in FIG. 10 has been conventionally used. However, there has been a problem that a conduction failure between the contacts occurs due to adhesion of a foreign substance to the contacts, or the like.
Therefore, JP-A-2000-322963 discloses a switch having a contact structure 300 in which a first contact is a doughnut-type contact 302a, and a second contact is a crossbar-type contact 302b that extends in a direction crossing the doughnut-type contact 302a as illustrated in FIG. 11.
A first contact is allowed to be the doughnut-type contact 302a in such a manner, whereby a conduction failure is precluded since the contact points between the contacts become many points and a foreign substance can be dissipated into the depression of the doughnut-type contact 302a even when entering between the contacts.
JP-A-2002-343207 discloses that a body-ground-type pressure switch configured so that one or a plurality of recesses are disposed in the upper portion of a protrusion 121 disposed on a guide portion 111, and electrical contact between a movable contact 118 and a protrusion 121 occurs on a plurality of contact points as illustrated in FIG. 12.